Random noise apparatus and method



INVENTOR.

14 7701 /Vf V5 E. J. HEBERT, JR

Filed April 17, 1956 RANDOM NOISE APPARATUS AND METHOD EUGENE cl Hgaaerde w H B p/ Z M. M f 7 E E N w r as .flm mm m W K M mm R AE E\ /0-Mr m M7 E U5 DHW W I'SA mm MN MW fig Z a m MM w WM 5w MA H U P Z 5m 1 R Y W W n ..H...,.H.....H. .v. Wm w E L r 5 WW I United States Patent RANDOM NOISE APPARATUS AND METHOD Application art, 1956, Serial No. 578,616

' 3 Claims. 01. 324-158) This invention relates generally to a random noise apparatus and method, and more particularly to a random noise apparatus and method which employ radioactive material as the primary noise source.

As is well known, noise apparatus has many applications in the field of electronics. For example, calibrated noise apparatus may be used as a standardvfor measurement of receiver noise figures. A random noise apparatus, entirely free of non-noise components, may be used as a modulation source for counter-measures equipment.

In the prior art, noise has been generated bye number of sources, including thermal (Brownian movement or Johnson noise), arc discharge, gaseous discharge, barrier layer contacts (crystals, oxides, etc.) and electrolytic sources. The prior art devices are unsatisfactory in that the noise level is such that it may only be determined by predicting the noise generated from a knowledge of the input and the characteristics of the device. The noise generated is unsatisfactory in that it is :not true random or stochastic noise.

It is a general object of the present invention to provide a random or stochastic noise source which makes use of radioactively emitted particles. 3 l I It is another object of the present invention to provide a random noise apparatus and method in which relatively large amounts of noise power and energy are generated.

It is still another object of the present invention to provide a random noise apparatus and method in which radioactively emitted random particles strike scintillating material to produce or emit photons which are received by photoelectric means to generate electrical noise.

It is another object of the present invention to provide a random noise apparatus and method in which the power generated is of such magnitude that the noise power applied to associated apparatus may be measured directly.

It is another object of the present invention to provide a random noise apparatus and method which is relatively free of non-noise components.

These and other objects of the invention will become more clearly understood from the following description and the accompanying drawings.

Referring to the drawings:

Figure 1 shows a block diagram showing the random noise apparatus being used to measure the noise figure of equipment.

Figure 2 is a side elevational view partly in section of the electrical noise generator.

Generally, a radioactive source serves to randomly emit particles which are employed to generate random electrical pulses. Thus, the particles may strike material which scintillates. Photoelectric means serve to convert the photon energy into electrical pulses. 1

Referring to Figure 1, radioactive material which serves to emit radiation particles may be any suitable radioactive material. For example, the material may be a material which emits beta particles and which has high chemical and radioactive stability. For example, radio- 2 active material may comprise vcarbon 1,4, technetium 99, cesium 135, nickel 63, Ihenium 187, etc.

The radioactive material 11 serves to radiate particles 12 which strike the scintillation material 13. As is well known, the material scintillates (emits photons) whenparticles impinge thereon. The electrons of the material are excited by the energy of the particles and radiate photons. Thus, some of the particles 12 radiated by the radioactive material strikethe scintillation material 13. Photons 14 are emitted.

Many types of material may act as photon sources of the character described. Scintillation crystals are well known in the art. Certain plastic compounds may also be used. For example, polystyrene monomers, dyphenylbutadiene, dyphenylacetylene, stilbenes, polyphenols, and

.phenylene oxides may be employed.

All of the materials described above with'tlieference to scintillating materials and radioactive materials have a long useful activity life, h gh speeds of response and stability.

It is apparent that photons will be radiated .in accordance with the impingementof particles into the scintilla- .13 then strike the photoelectric means '16 which serve to convert the light energy into an electrical signal. Thus, as illustrated, the photons strike the cathode of.the photomultiplier tube 16. This causes emission of electrons at the cathode. The electronflemission is multiplied by the anodes of the photomultiplier tube in amanner well known in the art.

Thus, the photomultiplier tube serves to amplify the emitted photoelectrons whereby an :amplified signal is produced. The:outputy:17 of the photomultiplier tube is in the form of electrical pulses which have an amplitude and time distribution which correspond to the energy and time distribution of the radiated particles. A suitable power source 18 is illustrated to supply driving potentials to the plates of the photomultiplier tube.

The random electrical noise is applied to an impedance matching network 19 which serves to present a suitable input impedance to the equipment under test 21. The impedance matching network comprises a passive network which is adjustable to provide the required impedance. The network may, for example, be a resistivecapacitive network in which the resistance and capacity are variable. An output impedance may be provided to the equipment under test which correspond exactly to the impedance into which the equipment would be normally connected.

In contrast to prior art equipment wherein the energy fed to the noise source was measured and the output noise predicted therefrom, the noise may be measured directly.

, An electronic calibration network 22 is connected to the impedance matching network whereby the noise output 23 from the impedance matching network is calibrated and controlled. Suitable measuring apparatus 24 is connected to receive the output from the equipment under test.

By way of example, if the noise figure of the equipment 21 is to be determined, the noise apparatus is disconnected and the output of the equipment 21 is measured. The noise apparatus is then connected and the calibration circuit is so adjusted whereby the calibrated output from the impedance matching network causes the reading on the measuring apparatus 24 to be doubled. It is then apparent that the added noise is equal to the noise of the equipment under test. The noise figure of the equipment under test may be readily calculated from this information.

Referring particularly to Figure 2, a suitable electrical noise source is shown. Thus, a photomultiplier tube 26 is enclosed within the shield 27. The shield 27 is formed of suitable material whereby radiation from the radioactive source to the surroundings is prevented. It

is, of course, to be understood that the level of radiation is not such as might be detrimental to human well being. Nevertheless it is advisable to provide shielding 27.

The radioactive source 28 is placed adjacent the scintillation material 29 which is viewed by the photomultiplier tube 26. The output of the photomultiplier tube is available at the terminal 31. The shield 27 also serves to shield the photomultiplier tube 26 from external light sources. The crystal 29 is preferably made transparent to its own light whereby all of the scintillations generated therein are viewed by the photomultiplier tube.

It is, of course, apparent that the source 28 and the scintillating material 29 may be formed as a single unit.

The radioactive material may be dispersed in the form of small particles within the material whereby emitted particles cause scintillations in the surrounding material. In certain instances it may be suflicient to employ a junction semiconductor device. As is well known, when radiation particles strike these devices, an electrical impulse is generated. Thus, the emitted energy from the radioactive source will be directly converted into an electrical signal.

It is to be understood that although a single embodiment of the invention has been described and illustrated, that other embodiments may be made without departing from the spirit and scope of this invention.

I claim:

1. Apparatus for generating random electrical noise suitable for use in electronic equipment comprising a source of radioactive material serving to emit radiations, a scintillating material disposed adjacent said radioactive material and serving to be scintillated by the emitted radiation, photomultiplier means adjacent to said scintillating material and serving to receive scintillations therefrom and convert the same into electrical pulses, and a shield completely surrounding said source, material and photomultiplier means, said shield serving to support the various parts to maintain the same in the cooperative relationship, said shield further serving to prevent irradiation from the source to the surrounds.

2. Apparatus for generating random electrical noise suitable for use in electronic equipment comprising radioactive material serving to emit radiations, scintillating material disposed adjacent said radioactive material and serving to be scintillated by the emitted radiations, photomultiplier means adjacent said scintillating material and serving to receive said scintillations and converting the same into electrical pulses, and a shield surrounding said radioactive material, scintillating material and photomultiplier tube.

3. A system for measuring the noise figure of equipment under test comprising a source of radioactive material serving to emit radiations, scintillating material disposed adjacent said radioactive material and serving to be scintillated by the emitted radiation, photo-multiplier means adjacent said scintillating material and serving to receive scintillations therefrom and convert the same into electrical pulses, a shield completely surrounding said source of radioactive material, scintillating material and References Cited in the file of this patent UNITED STATES PATENTS 2,411,553 Ramo Nov. 26, 1946 2,620,438 Cotsworth III Dec. 2, 1952 2,755,389 Jones et al. July 17, 1956 2,772,368 Scherbatskoy Nov. 27, 1956 2,783,386 Mandeville et al Feb. 26, 1957 

